Quail populations in the early 20th century were a function of everyone living scattered about the southeast (more rural folks per acre by far then than now) and killing and eating everything that walked or flew. However, the habitat was FAR superior in quantity than now. The southeast was basically recovering from the cut-out and get-out era and everyone burned every spring. I would say habitat was the driver and lack of predators was an influential secondary.
I've heard the habitat argument over and over, especially the part about needing more contiguous acres of quail habitat. But I've done mapping work on some of the big quail plantations in south GA--20,000 contiguous acres of exceptional quail habitat--and they still struggle to keep viable populations of wild quail. The big difference between now and the "glory days" of quail was massive predator control. In those days, not only were predators trapped for fur, the government offered bounties on some of those predators, which put food on a lot of rural tables. In addition, in those days, it was common practice for farmer to shoot every hawk they saw. While working on a quail-managed property on the GA coast, I watch hawks pick off quail after quail.
